SYDNEY (REUTERS) - Australia on Thursday for the first time exercised sweeping new security powers allowing it to block citizens from travelling to overseas conflict zones such as those in Iraq and Syria, where dozens of Australians have joined Islamist militant groups.

Foreign Minister Julie Bishop designated the Islamic State in Iraq and Syria's (ISIS) stronghold of Raqqa province in Syria off limits as part of a push to combat what the government says is growing radicalisation among young Australian Muslims.

It is the first use of new security powers obtained by conservative Prime Minister Tony Abbott, under which Australian citizens travelling to any area overseas declared off limits can face up to a decade in prison.

"Under the provisions of our foreign fighters legislation, I have today declared Al Raqqa province an area where a listed terrorist organisation is engaging in hostile activity," Bishop told Parliament.

"This now makes it an offence under Australian law to enter or remain in the province of al-Raqqa without a legitimate reason. Anyone who enters or remains faces a penalty of up to 10 years' imprisonment."

In September, the United Nations demanded that all states make it a serious criminal offence for their citizens to travel abroad to fight with militant groups, or to recruit and fund others to do so, in a move sparked by the rise of ISIS.

Security analysts have put the number of foreign fighters in Iraq and Syria, travelling from scores of countries around the world, in the thousands.

Australia is on high alert for attacks by radicalised Muslims or by home-grown militants returning from fighting in the Middle East, having raised its threat level to high and undertaken a series of high-profile raids in major cities.

Abbott has said that at least 70 Australians were fighting in Iraq and Syria backed by about 100 Australia-based "facilitators".

The government, which recently warned that the balance between freedom and security "may have to shift", is also introducing controversial data retention laws it says are needed to tackle security and criminal threats.

Critics say the data laws go too far in compromising privacy, will be too costly and could lay journalists and whistleblowers open to hefty prison sentences.

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